Voice over Internet (i.e. VoIP) communication terminals provide the capability to receive both voice mail messages and conventional email or data messages. Such systems may incorporate unified messaging. In unified messaging, voice messages show up as items in an email inbox.
When the client, i.e. user, retrieves the voice message, a file is read from the message stored in the communication terminal and sent across the communication network to the message server to retrieve the voice message stream. The message server includes an inbox which stores the voice messages for the user.
The inboxes in a unified messaging system are accessed from the message server over network connections, e.g. Internet network connections, having varying speeds, i.e. bandwidths or data transfer rates. As a result, a single encoding, i.e. digital conversion, for voice messages is not suitable for all speeds. For example, the G.711 encoding protocol has a bit rate of 64 kbit/s. This bit rate is suitable for transmission over an office LAN, but will be constrained and too slow over a 28.8 kbit/s dial-up network connection.
Various approaches have been tried in the art. One approach involves always using the lowest bit rate codec (Coder/Decoder) for storage. But when there is abundant bandwidth in the network connection, there will be extra transcodings, i.e., conversions between different codecs or voice compression formats, which increases the load in the messaging system. Transcoding also degrades voice quality.
Another known approach comprises a per user configuration. If a user can access a unified messaging system over a slow dial-up network connection, then all of the user's messages are stored using a low bit rate codec, i.e. tailored to the bandwidth of the dial-up network connection. However, this means that the voice quality the user gets if accessing the unified messaging inbox using a broadband (i.e. high bandwidth) network connection will be a lower voice quality for the voice message. For example, a user in the office configured with a low bit rate codec (e.g., for dial-up access) will experience lower voice quality than a co-worker who has voice messages configured for broadband access, even though both office workers are accessing their messages over the same LAN in the office. Furthermore, a user who is not configured with a low bit rate setting (i.e. low bit rate codec) might want to access their unified messaging inbox over a network connection from a hotel.
Yet another approach involves allowing a voice message to appear several times in the unified messaging inbox, with each appearance corresponding to a particular encoding (i.e. codec). The user then decides on which encoding to use by selecting the appropriate appearance, e.g. icon, of the voice message. It will be appreciated that this approach tends to clutter up the user's inbox, and requires the user to correlate the available bandwidth capacity with the appropriate voice message icon. Furthermore, when any one version of a message is deleted, all of the other versions of the message must also be deleted or erased.
In view of these deficiencies in the art, there remains a need for a mechanism for varying encoding of voice messages in a unified messaging system.